Most aircraft, particularly civilian transport airplanes, comprise an autopilot allowing the aircraft to be flown automatically without action on the part of the pilot, for example during phases of cruising flight. The pilot is thus relieved from his flying tasks during these phases of cruising flight which may last for several hours on long-haul flights. When he so wishes, the pilot can deactivate the autopilot in order to take back control of the aircraft himself. The pilot generally has a button that he can press in order to deactivate the autopilot. In the case of airplanes of the Airbus A320, A330, A340 etc. type, this button is located on the mini-stick used for controlling the movements of the airplane. There are also circumstances in which the autopilot is deactivated, independently of the pilot's volition (autopilot fault etc.) or without the autopilot deactivation button being pressed (in the event of action on the rudder pedals, action on the mini-stick, etc.). In all cases, a warning is activated in the cockpit in order to alert the pilot to the fact that the autopilot has been deactivated, in case this deactivation was unintentional or not instigated by the pilot, and has passed unnoticed. This warning is generally made up of visual warnings (the displaying of text messages and the activation of warning lights) and of an audible warning.
However, this audible warning may distract the pilot in his activities, particularly when the autopilot has been deactivated deliberately at the pilot's initiative by pressing said button. In order to stop this audible warning from being emitted in the cockpit, the pilot can acknowledge it by pressing said button. The pilot is therefore asked to acknowledge this audible warning by pressing this button a second time if the autopilot has been deactivated deliberately or by pressing this same button for a first time if the autopilot has been deactivated unintentionally or not at the instigation of the pilot. This method of operation has the disadvantage that if the autopilot has been deactivated because the pilot has unintentionally pressed said autopilot deactivation button twice, no audible warning is emitted in the cockpit. In such a case, the pilot may be unaware that said autopilot has been deactivated, and this may be detrimental to the flight of the aircraft.
These problems are solved, at least in part, according to the invention by a method for producing an audible warning when an aircraft autopilot is deactivated. This method is noteworthy, in that it involves the following steps:                a) emitting a first sound in the cockpit of the aircraft for a period of time ranging between a first predetermined value and a second predetermined value;        b) emitting a second sound in the cockpit of the aircraft.        
In this way, because the first sound is emitted for a minimum length of time corresponding to said first predetermined value, an audible warning is emitted in the cockpit irrespective of the circumstances in which the autopilot was deactivated, particularly even if this deactivation is the result of the deactivation button being pressed twice unintentionally. This allows the pilots of the aircraft to be better aware of this warning (and therefore of the fact that the autopilot has been deactivated).